Macroscopic Distinguishable States of Mechanical Oscillators Generated by Quantum Nondemolition Measurements

Abstract

The implications of quantum mechanics on the realism in the macroscopic world have been outlined from the early development of the theory.1–3 In more recent times the feasibility of experiments capable to answer some questions originated from the Schroedinger-Einstein debate has been discussed with particular emphasis on the possibilities offered in the quantum optics framework.4 It has been shown that a quantum non demolition monitoring can generate macroscopically states in the optical range, i.e. optical Schroedinger’s cats.5 On the other hand quantum non demolition strategies have been originated for monitoring macroscopic mechanical oscillators and thus may open the unique opportunity for monitoring a single, macroscopic system at the quantum level of sensitivity. We discuss here the possibility to generate macroscopic distinguishable states through quantum non demolition measurements on mechanical oscillators monitored by means of electrical quantities. In section 2 we recall the quantum non demolition strategies for a phonon-photon coupling with a particular care to the stroboscopic techniques.6 In section 3 we discuss electromechanical transducers based upon electron tunneling. The high speed of such a kind of transducers allows to implement quasi-stroboscopic quantum non-demolition techniques. In section 4 we discuss the feasibility of experiments in which distinguishable states are generated in a macroscopic mechanical oscillator through a quasi-stroboscopic quantum non demolition coupling to an electromechanical vacuum tunneling transducer and some of the problems that can arise in such a detection strategy.